The present invention relates to a circuit and method for adjusting a data detecting level of a disk driving apparatus, and more particularly, to a circuit and method for variably adjusting the data detecting level.
Generally, disk driving apparatus such as a hard disk drive, a floppy disk drive, etc. is widely used as an auxiliary memory of a computer system. Disk driving apparatus record data only a hard disk or a floppy disk, for example, and read the recorded data. In reading the recorded data, a signal picked up by a head of the disk driving apparatus is hysteresis-compared with a predetermined data detecting level in a read processing circuit, in order to detect the data.
In one typical contemporary design of a circuit, a signal picked up from a disk by read heads of a disk driving apparatus is amplified, filtered, and simultaneously applied to a differentiator and rectifier circuit. The rectifier circuit detects the voltage level of a signal by full-wave rectifying the filtered signal and the voltage level detected is applied to automatically control gain control gain of a control amplifier. The differentiator detects the peak value of the signal by differentiating the filtered signal. A pulse signal is generated in response to the peak value detected by the differentiator. The differentiator may however, undesirably provide false output data when, for example, the filtered signal contains noise. In order to prevent output of false output and to restrict detection to only data exhibiting the peak value, the differential comparator hysteresis-compares the filtered signal with a predetermined data detecting level SETHYS provided by a data detecting level adjusting circuit. A differential amplifier generates a signal in response to the filtered signal. A flip-flop generates a signal by latching the output signal from the differential comparator at a rising edge of the signal generated from the first bidirectional monostable multivibrator. Then, a second bidirectional monostable multivibrator is triggered at the rising and falling edges of the signal provided by the flip-flop to produce a pulse signal. When comparing the filtered signal with the pulse signal, only the peak value is detected. Hence, the pulse signal generated from the second bidirectional monostable multivibrator is produced as data.
Actually, the signal picked up by the heads varies depending upon operating circumstances such as the interference, impact, noise of the signal, and the like. In particular, as the capacity of the disk increases, the recording information of the disk is highly packed; and as the number of tracks increases, the signal is severely varied. Therefore, if the data detecting level is inappropriately given, a data error is generated. That is, if the data detecting level is too high, a data loss part P.sub.mis occurs, and if the data detecting level is too low, a data noise part P.sub.ext is detected. Thus, in consideration of the variation of the signal, the data detecting level must be set to an appropriate value by the data detecting level adjusting circuit.
In one example of a conventional data detecting level adjusting circuit, the data detecting level is adjusted by using a resistance voltage divider to divide a supply voltage Vcc to a uniform value. The resistances of the divider are selected so as to provide an appropriate data detecting level.
Meanwhile, the size of the signal picked-up by the head in the disk driving apparatus also differs as a function of the position of the disk and each disk driving apparatus. Since the data detecting level adjusting circuit has one fixed data detecting level, different resistances must be selected for different apparatus. Hence, each disk driving apparatus must be modified in its hardware, and it is difficult to prevent the data error caused by the variation of the signal according to the position of the disk, or operating circumstances.
In order to solve such disadvantages, a technique disclosed in Korea Patent Application No. 92-22630 assigned to the same assignee of the present invention, uses selection of three predetermined data detecting levels. Thus, during a test process when manufacturing the disk driving apparatus, the data detecting level is varied in response to the area of the disk and simultaneously a sector or a data interval in which an error occurs is mapped to a defect list. Then, when a user operates the disk driving apparatus, the data error caused by the variation of the signal by the defect of the disk is prevented. Korean Patent Application No. 92-22630 however, has problems in that hardware must be modified as a function of each apparatus because the data detecting level is still fixed; moreover, it is difficult to prevent the data error caused by the variation of the signal by operating circumstances.
In U.S. Pat. No. 5,150,050 for Adaptive Variable Threshold Qualification Level Circuit For Signal Processing In Disk Drives by Stephen R. Genheimer and Steven L. Welty, a microprocessor generates a qualification level signal by retrieveing selected optimal qualification level signal data from its memory, or alternatively, by interpolation. A qualificaton level generator provides a variable qualification level signal, while a threshold detector receiving a raw data signal ostensibly representative of data to be read from a magnetic disk through relative movement between a magnetic transducer and addressible portions of the disk, compares the raw data signal to the qualification level signal in an effort to detect amplitude errors when the raw data signal does not meet the qualification level. When an amplitude error signal is detected, the microprocessor varies the qualification level signal as a function of whether a low amplitude read error or an extra amplitude error is detected, and causes data stored on the on the addressible portions of the disk to be re-read once the microprocessor has varied the qualification level signal. In this process however, it is necessary to first map defects of the magnetic disk using a variable qualification level signal, identifying errors caused by reduced signal amplitude by setting the qualification level signal to a desired level above the normal qualification level for the specific track and errors caused by extra amplitude by setting the qualification level signal to a desired level below the normal operational level, and mapping the errors detected into a memory of the controller. Moreover, it has been my observation that in this circuit, the qualification level signal is, in essence, a constant value relative to each track.